1. Field of the Invention
This invention relates generally to systems and method for reading data from and writing data to data storage medium by employing the magnetic or optical recording technology. More particularly, this invention is related to a data access system implemented with stepping motors using open and closed control loops to position a flat medium with data stored in discrete stepwise curved segments accessed by a rotational pickup head controlled with servo data feedback from each stepwise discrete segment.
2. Description of the Prior Art
Conventional methods of reading data from and writing data to data-storage tracks with these tracks formed either as circular tracks or separate segments as parts of a circular track present technical difficulties when stepping motors are employed for moving the pickup head to access high density data tracks. Due to these technical difficulties, stepping motors moved in discrete stepwise movements and controlled with open-loop control schemes, are typically implemented in data-access operations of lower data density. In a data track, typically a circular track, that has a lower data storage density the spot size for data-bit storage is large enough to accommodate a larger tolerance of radius variations as the disk rotates over a pickup head for accessing data stored in the data tracks. For this reason, an open-loop control would be sufficient for carrying out the data access functions by moving a data disk or a pickup head in a stepwise manner to a particular track on a relatively low track density device such as a conventional floppy disk. And, the pickup head is applied to read or write data on that track without further position control of the data access functions. It is expected that the circular track or arc segment(s) prescribed by the pickup head would match the data-storage track formed either as a circular track or circular segment.
Based on these operational principles, there are many prior art disclosures for data recording and access systems implemented with group of concentric circular data tracks. Prior art patents disclose the storage and data access technologies in U.S. Pat. No. 3,596,061 issued on Oct. 14, 1968 to Pasini, U.S. Pat. No. 5,526,328 issued on Jun. 11, 1996 to Oshima et al., and U.S. Pat. No. 6,052,347 issued on Apr. 18, 2000 to Miyata et al. In addition to the concentric circular data tracks, continuous circular or linear segments employed for data storage and access are also known in many prior art disclosures. These disclosures provide group of data tracks as circular arcs or linear line segments to store and retrieve data on a flat media. The prior art patents include U.S. Pat. No. 3,716,678 issued on Nov, 9, 1970 to Starr, U.S. Pat. No. 3,598,965 issued on Aug. 10, 1971 to Nagata et al., U.S. Pat. No. 5,107,099 issued on Apr. 21, 1992 to Smith, U.S. Pat. No. 5,963,513 issued on Oct. 5, 1999 to Lemelson, U.S. Pat. No. 6,016,959 issued on Jun. 25, 2000 to Kamo et al., U.S. Pat. No. 5,521,774 issued on May 28, 1996 to Parks et al., U.S. Pat. No. 6,084,850 issued on Jul. 4, 2000 to Gudesen et al., U.S. Pat. No. 5,045,676 issued on Sep. 3, 1991 to Kime, U.S. Pat. No. 4014604 issued on Mar. 29, 1997 to Schwartz, U.S. Pat. No. 5,059,774 issued on Oct., 9, 1991 to Kubo et al.
These earlier teachings use oscillating pivot rotating arms or oscillating flat media to access such plurality of data tracks. Smith (U.S. Pat. No. 5,107,099) teaches a method of rotating flat media and a fixed head mechanics to produce and retrieve such plurality of data arc tracks in the circular arc forms in additional to the mechanics of oscillating pivoted rotating head arm to a fixed flat media. Gudesen (U.S. Pat. No. 6,084,850) further extended such rotating media arrangement. Smith (U.S. Pat. No. 5,107,099) failed to teach the using of full rotational head mechanics to a flat media. Kamo (U.S. Pat. No. 6,016,959) recognized the full rotational head mechanics to produce and retrieve such plurality of data tracks in the circular arc forms. Kamo insists such mechanics requiring one or multiple pair of such rotational heads together to achieve such result even only one or more head is active for data access, one or more dummy head must be used to pair odd number of active heads. Kamo also teaches the loading of flat media to the mechanic in static mode that engage to pickup head at the placement of flat media to the device and disengage the pickup head at the removal of the flat media from the device.
For data retrieval and recording access, some of prior art teachings apply open loop to place the signal pickup head to desired data tracks under a relative low track density arrangement and expect the prescribed arc segment by the pickup head matches the recorded data circular arc. When the data track density becomes relative high, prior teachings use closed loop design or servo method to place the signal pick head to the desired data area that follows the profiles of recorded track. The track profile is expected to be a continuous circular arc or line. When a stepper motor is applied into track following, the motion of a stepper motor is discrete. The continuous track following of data segments becomes very difficult and almost impossible. Usually the radius of rotating head of servo writer is different from a drive, the continuous track following by the drive head along a servo written track is physically impossible by a stepper motor access mechanism that can only provide discrete motions.
Specifically, when the data-storage density is increased and a stepping motor is employed, technical difficulties arise due to the discrete and open loop features of the stepping motor movements. A continuous circular movement of the pickup head rotating over the data storage medium may not precisely track the profile of the actual locations of the stored data written onto the data storage medium. The difficulties of continuous track following of the data segments or a circular track can be clearly appreciated because the radius of the rotating head of a servo writer is different from that of a data drive. In addition to the difference in radiuses between that of the servo drive from that of a data drive in reading or writing the data, there are also differences of radius between every two drives used in writing and reading a data card. When the density of data storage becomes higher and the tolerance of data track following is reduced, implementation of stepping motor to adjust a relative position between a pickup head and a circular track or circular segments becomes impractical. For these reasons, the conventional circular track or arc segments as part of a circular track are no longer suitable.
In addition to the above difficulties, the rotational head data recording and retrieving system as that disclosed in a co-pending patent application is implemented to resolve the difficulties of the conventional technology. Specifically, in conventional data storage systems, the reading and writing of data are performed on concentric circular data tracks. The concentric data track configuration often presents a problem that the data-bit density varies between the outer tracks and the inner tracks. The variable bit density in data storage is due to a geometrical factor that the outer data tracks are much longer in length than the inner tracks. A common practice is to form the inner tracks with a capacity to store the data bit at a higher bit density. A more complicate servo control system implemented with more complex signal-processing algorithms is required due to the variations of data storage density between different data tracks. Additionally, by varying the data storage density from the inner tracks toward the outside tracks, the data transfer rate is also changed in accessing data from the inner tracks then outside tracks. Such variation may also cause difficulties and complications in processing the data. Higher error rates may incur due to these variations between the inner tracks and the outer tracks.
There have been designs using pickup head with oscillating arm to prescribe multiple parallel data arcs at a flat data media and a constant data recording density for easier data access arrangement. There are also designs to use single or multiple rotating head pairs to prescribe multiple data arc segments on a circular track and/or on such multiple parallel track arrangements. All such designs required either pickup head with oscillating arm or head pairs configuration. All prior designs also require that the flat media to be statically positioned to signal pickup heads once the flat media is engaged or inserted to the device.
An invention implemented with a rotational-head for data recording and retrieving as that disclosed in a co-pending patent application is able to resolve the above-described difficulties of uneven data storage densities. However, the difficulties in track following to accurately adjust the position of a pickup head relative to the data tracks can not be resolved by the techniques disclosed in all of the prior art disclosures discussed above in a data access system implemented a stepping motor with open-loop discrete movements.
Therefore, a need still exists for an improved data access system and data-card operated with new configuration and control loops to overcome the technical difficulties as described above. Specifically, the storage card drive system shall provide a uniform density for data storage. Also, the data card should provide a data tack configuration to conveniently implement a open and closed loop control scheme for precisely adjust the position of a pickup head relative to the data tracks for achieve a track following to access data for high density data tracks. Furthermore, it would be desirable to keep the system portable and can be manufactured with reasonably low cost such that the data access devices can be broadly employed with lower cost barriers.
Therefore, an object of the present invention is to provide a data storage-card drive system with single pickup head moving above the data-storage card in rotational movement. In order to take advantage of a more cost effective configuration by employing a stepping motor for accessing data stored in high density data tracks, special open-and-closed loop control mechanisms are applied with specially arranged servo and data segments for accommodating the stepwise offsets between the servo and data segments. The new data segment arrangements and pickup head control schemes provide a solution to enable those of ordinary skill in the art to use a stepping motor to read data from high density data tracks thus resolves the difficulties encountered in the above mentioned prior art technologies.
Specifically, it is an object of the present invention to provide a data-storage card drive system with single pickup head driven by a motor, e.g., a brushless motor, to rotate over the data-storage card with the rotation axis perpendicular to the card surface. The motor is mounted on a carriage for making vertical movement perpendicular to the data card for engaging and disengaging a signal pick up head to a flat media per data retrieving and recording configurations. An X-Y table is engaged to a stepping motor to discretely move and position the card on the center relative to the rotation of the pickup head. In addition, the discrete movements of the X-Y table is to position the selected data track under a signal pick up head for properly carrying out the data retrieving and recording processes. The data card is formed with a plurality of data track with each track broken into many discrete stepwise segments and each discrete stepwise segment includes a servo segment and a data segment. The data segment and the servo segment are biased from each other with slightly different curvatures. The servo segments provide position and sector offset and position error data as close-loop feedback for controlling the discrete motion of the X-Y table to prepare the pickup head to read the data from the data segment with an open loop control scheme.
Briefly, in a preferred embodiment, the present invention discloses a data card that has a plurality of data tracks disposed on a flat data storage medium. Each of the data arcs further includes a plurality of stepwise discrete segments. Each segment includes a servo segment and a data segment. Each of the servo segments is substantially a circumference segment of a first circle and each of the data segments is substantially a circumference segment of a second circle where the first circle and the second circle has different radius. In a preferred embodiment, the second circle has a substantially equal or slightly shorter radius than the first circle. In another preferred embodiment, the second circle has a substantially equal or slightly longer radius than the first circle. The present invention also discloses a data access system for access data stored on a flat medium. The data access system includes a pickup head rotating over the flat medium. The data access system further includes a stepping motor for discretely moving the flat medium substantially along a lateral direction perpendicular to a rotational axis of the pickup head. In a preferred embodiment, the data access system further includes a closed loop control mechanism for controlling the stepping motor for reading data from a servo segment on the flat medium. The controller further includes an open loop control mechanism for controlling the pickup head for reading data from and writing data to a data segment on the flat medium.
These and other objects and advantages of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiment which is illustrated in the various drawing figures.